This program is designed to provide a multidisciplined approach to the study of the physiological significance of in vitro blood rheology studies. The long range goal of the proposed research is to contribute to the understanding of the rheological properties of blood to: 1) the flow of blood in vivo; 2) the diagnosis and treatment of clinical disorders associated with potential rheologic alterations. The specific aims of the present program include: 1) studies of the flow behavior of erythrocyte suspensions in geometries relevant to the microcirculation, including narrow bore glass tubes and portions of an in vitro flow replica derived from a microcirculatory bed; 2) continued physical-rheological analyses of the effects of storage of human blood intended for transfusion; 3) rheological studies of selected erythrocyte populations whose age, chemical-modification, metabolic state or shape make them relevant to the interests of the Research Program; 4) macro-and microrheological evaluation of blood from patients whose disease alters the rheology of blood and the use of selected hemorheological data as supporting information for patient care. Successful completion of the major aims of this program should provide; 1) quantitative information relevant to the prediction of pressure-flow-relations in a vascular bed based on in vitro rheologic data; 2) detailed data regarding the macro- and microrheological properties of stored and pathologic blood; 3) insight into the use of various rheological parameters as diagnostic and supportive information for patient care. Of long range significance is the potential contribution with studies of this type may make to clinical medicine; if syndromes of "hyperviscosity" are to be utilized with scientific meaning, a clearer understanding of their etiology, rheologic mechanisms and physiological import is essential.